One human anti-lymphocyte serum can exhibit many different types of reactivity. The anti-HLA activity may be "monospecific" or may cross react with antigens not present on the immunizing cell.. Studies on the interrelationships of these reactions using standard immunologic separation techniques are often ambiguous. The purpose of the proposed research is to exploit the potential of IEF in separating the components of cytotoxic anti-lymphocyte reagents so that the properties of each may be studied separately. IEF is capable of separating antibodies against the major specificity from antibodies reacting against both the major and the crossreacting specificity in HLA. We have prepared a specific anti-A2 reagent from an antiserum which reacts with virtually every test cell. The multispecific antibody focuses at the anodal end of the IEF gradient and the specific anti-A2 antibody focuses at the cathode.